C program to draw exponential curve

For the Cavendish experiment, we'll need to fit our data to a sinusoidal curve with exponential decay. How to plot linear, cubic and quadratic fitting curve in a figure?. (b) Draw a bracket (or just imagine it) to indicate where y has 100% (or all) of its initial value. Use sliders to change the parameters. Try it yourself. There are two parameters. Curve fitting is the process of constructing a curve, or mathematical function, that has the best fit . Depending on the algorithm used there may be a divergent case, where the exact fit cannot be calculated, or it might take too much computer   Fit exponential models in Curve Fitting app or with the fit function. 2. V4. So let's say we have y is equal to 3 to the x power. New is an exerciser program allowing step by step observation of the curve fitting process. 1 Fit XYYYY Data and Plot Each Fit in Separate Window; 1. Press ENTER twice and the exponential regression program will be run. 7763/IJCEA. Hissein, and S. 2. . But sometimes, you will need to do exponential calculation to a range of cells, how can you apply exponential calculation in Excel? Function Curves. I have a run an experiment using my C program. . 74. How to Draw Curved Lines in Photoshop. Area Under a Curve from First Principles. I'm very new to the Math. A 1-d sigma should contain values of standard deviations of errors in ydata. If you now plot the graph of time vs distance, you've plotted the function distance=e^time. Graph exponential functions and find the appropriate graph given the function. Jan 2, 2014 Tags:c/c++, exp, exponential function, math exp Using Faster Exponential Approximation C/C++ double faster approximation be so noticeable because the value itself is so tiny that can't be observed visually in graph. May 16, 2014 C Program for Linear/Exponential Curve Fitting, with short and simple source code in C language for both curves and output. INSTALLING AND STARTING GNUPLOT - version 4. In the diagram above, a "typical rectangle" is shown with width Δx and height y. values and constraint bounds appropriate for your data, or change algorithm settings. rules applied to Standard Curves Analysis Introduction. So, the user doesn’t need to give any input to the program. The code below  e is the base rate of growth shared by all continually growing processes. e . The effects of a, p and q on an exponential graph Finding the equation of an exponential function from the graph . The slope of a secant line is also known as the "average rate of change. This means that the equation of the line of best fit is approximately y = 1. 1) even though product accumulates The important parameters of the function curve() used in this call are as follows: An mathematical expression as a first parameter. Its area is yΔx. Microsoft Excel does not have native calculus functions, but you can map your Real-Time PCR Applications Guide Initially, fluorescence remains at background levels, and increases in fluorescence are not detectable (cycles 1–18 in Figure 1. 5 Responses to “C Program to implement Bezier curves for a given set of control points. Check to make sure that it fits your entire selected dataset. Try different fit options for your chosen model type. Select File > Generate Code. All the C functions, constants and header files have been explained in detail using very easy to understand examples. There are two algorithms used for curve fitting within SLIM Curve: The first is a triple integral method that does a very fast estimate of a single exponential lifetime component. It replaces the old article, which can be found . In the project we will investigate exponential functions, exponential growth and decay, Here is a family of exponential functions with the same initial value (C), but differing growth rates (1/5, 2/5, 3/5,,2). employees that post about their personal lives b. DOI: 10. This not exactly a exponential probability density calculator, but it is a cumulative exponential normal distribution calculator. • Problem: Regarding the fitted curve for Excel’s Exponential Trendline, I need help on creating a formula that would create an exponential curve like the one illustrated on the file 'Exp Curve'. Input/Output: Also see, Numerical Methods Tutorial Compilation. Label the axes but don’t put any numbers on the axes yet. First, notice that the curves always sum to 1. we go on Here is a plot the data points and the least squares line : . graph, plot, pic2plot, tek2plot, and plotfont, and the mathematical programs spline, ode, and . This document is a handbook for using QtiPlot, a program for two- and three- dimensional graphical 2D plot from function. Not long ago, a client wanted to fit a set of data points to a Weibull curve of the form: The earlier example Find an exponential least squares fit for a set of points in C# explains how to find a least squares fit for exponential data. In the Curve Fitting app, select X Data and Y Data. • In Excel, you can create an XY (Scatter) chart and add a best-fit “trendline” based on the exponential function. This code can be entered in the MATLAB command window or run from an m-file. Anyone who wants to draw graphs of functions will find this program useful. At the top of the window, click Chart, Add Trendline, and Exponential. Suppose that the time that elapses between two successive events follows the exponential distribution with a mean of $$\mu$$ units of time. , select Polynomial. 8 Output via printf() Function Below is a simple C program that illustrates the important programming constructs (sequential Exponent shall be an integer. 1 Linear Fit. The KaleidaGraph Guide to Curve Fitting 6 1. a normal distribution 19. (It may not be entirely obvious, but it's true. Then calculate the mean. Exponential curve fitting, like power-l aw fitting, is a good example of a technique in which linearization would work if you already knew the exponent – but you don’t. See the texbook "Applied Calculus" by Waner & Costenoble for a method to obtain such a best-fit curve. Decline curve analysis is the most currently method used available and sufficient . g. The Standard Curves macro in SigmaPlot provides five equations that may be fit to your data. In this program, there is a fixed density value, as well as fixed start and end values for the linear fog. When a curve is high, the weight is high and the associated control point has a lot of influence: a lot of pull. Sign changes will flip the third degree curve top for bottom in shape. In linear mode, a straight-line baseline connecting the two ends of the signal segment in the upper panel will be automatically subtracted before the iterative curve fitting. It is apparent from looking at the data that "a" is about 1 and "b" is about -2. I have written a code to curve fit some data and calculate time and rate constants for the exponential recovery for some data. c. Notice, this isn't x to the third power, this is 3 to No plotting program would be complete without the ability to fit our data to a curve. The Exponential Curve, Phase II I haven't posted anything for a couple of years now, and I think I'm finally able to start up again. Exponential decay occurs when a population decreases at a consistent rate over time. $$10. You can use the model to gain evidence that that the model is valid by seeing whether the predictions obtained match with data for which you already know the correct values. We recommend that you use this dialog to include all your frequently used curves to a library so that you can use then conveniently in other studies and documents. A Bézier curve (/ ˈ b ɛ z. The curve fitter calculates the best fitting exponential function given a set of Then click the [GO] button to calculate the a,b,c parameters and paint the graph. In the flat mode, a constant baseline is included in the curve fitting calculation, as described above. Hello Friends, I am Free Lance Tutor, who helped student in completing their homework. 1 The C application programming interface. We saw how to check for non-linearity in our data by fitting polynomial models and checking whether they fit the data better than a linear model. Using R for Statistical Tables and Plotting Distributions The Rsuite of programs provides a simple way for statistical tables of just about any probability distribution of interest and also allows for easy plotting of the (a) Draw a smooth decay curve from upper-left to lower-right. Graphing Exponential Functions . Source: How to Find the Area Under Curve in Microsoft Excel Sample question:Find the area under curve in Microsoft Excel for the graph below, from x=1 to x=6. However, by the nature of exponential functions, their points tend either to be very close to one fixed value or else to be too large to be conveniently graphed. Computing Descriptive Statistics for Multiple Variables Calculating Modes Identifying Extreme Observations and Extreme Values Creating a Frequency Table Creating Plots for Line Printer Output Analyzing a Data Set With a FREQ Variable Saving Summary Statistics in an OUT= Output Data Set Saving Percentiles in an Output Data Set Computing Confidence Limits for the Mean, Standard Deviation, and Graph is an open source application used to draw mathematical graphs in a coordinate system. Now let’s see how to fit an exponential model in R. 2 Nonlinear Curve Fits Nonlinear curve fitting is accommodated in KaleidaGraph through the General curve fit function. C library function exp() - Learn C programming language with examples using this C standard library covering all the built-in functions. More specifically I intend to use this function: f(x) = a*exp(b*x) + c*exp(d*x) Using MATLAB I get pretty good results, as shown in the following image: MATLAB calculates the following parameters: To plot an exponential function, what you can do is type in your function. " Choose "a*exp(b*x)" as your fit. Although many types of probability density functions commonly occur, we will restrict our attention to random variables with Normal Distributions and the probabilities An exponential function that goes up from left to ri ght is called “Exponential Growth”. 1 describe exponential growth . I have already tried to model this curve in MATLAB using the built in function 'polyfit' and to graph it using 'polyval'. curve can plot also an expression in the variable xname, default x. In the applet below, move the sliders on the right to change the values of a, b and c and note the effects it has on the graph. Pressing the left mouse button chooses between 3 types of fog: exponential, exponential squared, and linear. The points determined in this way are then joined with straight lines. Modeling and graphing using MATLAB was successful :) . You can also modify other equation settings and options from this panel by clicking Options, which opens the Equations Options dialog box. The exponential decay curve, for example, can be linearized by taking logarithms: Log(y)=a'-b*x. Press [WINDOW]. Export QtiPlot windows/projects as Origin C files; 1-14. What can I say? R makes it easy to draw probability distributions and demonstrate statistical concepts. «1x». We need to create a small bin data series (for example with bin of 0. gnuplot supports these nonlinear curve fits, and can even take the experimental uncertainties of the data points into account. link brightness_4 code Jun 1, 2018 Exponential Fitting – C PROGRAM. fn(x) or expr (with x inside) must return a numeric of the same length as x. The Fit Exponential Decay Second Order dialog box. Prediction of Reservoir Performance Applying Decline Curve Analysis . a power law distribution d. plot(x,y) Probability Plots for Teaching and Demonstration . We will use putpixel functions of graphics. Suppose that your market research of . formula ( notice e used for exponential decay in value) or radioactive decay. ie,fit a curve then plug both vectors into your least-square program C Program to draw a rectangle and perform the operations. ) When a curve is near zero, the control point has little influence. employees that mostly post about products c. Sketch the graph of y=ax2+bx+c for:. I have been running into some problems curve fitting the data, and I cannot figure out where the problem is. First of all we need to find a formula for inverse probability distribution, search one in office formula list. Rahuma, H. The above given source codes in C language for curve fitting are applicable for linear and exponential approximation of available data or for fitting linear or exponential curves through easy, accurate and fast way. I have been using GNU plot to plot histograms/graphs to analyse the data. Excel is a good utility program for data recording and plotting, and is actually used a lot by C Language: exp function (Exponential) In the C Programming Language, the exp function returns e raised to the power of x. Source code: fog. In this post I will be showing you how to write a code that fits the data-points to an exponential function, like: Exponential Functions. SLIM Curve is used for FLIM functionality in the Advanced Technology Group's Time Resolved Imaging (TRI2) software, as well as in the SLIM Curve plugin for ImageJ. 3 Choosing a Curve Fit Model 1. a bell curve c. A logarithmic function has the form: We can still use LINEST to find the coefficient, m, and constant, b, for this equation by inserting ln(x) as the argument for the known_x’s: an R(x) curve for each pair of values, and then ee which pair best matches your experimental data, but this approach would clearly be very tedious. In this video, I want to introduce you to the idea of an exponential function and really just show you how fast these things can grow. Then we can sim Introduction to R I. Hi R experts, Could you please help me to fit a linear, cubic and quadratic curve in a figure? I was trying to show all these Plotting and graphing are methods of visualizing the behavior of mathematical functions. The blogs that draw the most readers tend to have all of the following characteristics except: a. These two parameters fully specify the command line that was used to invoke the executing program. Changing b alters the curvature of the parabolic element, and changing a changes the steepness of the cubic "s" curve. Enter the given exponential equation in the line headed “Y 1 =”. peak-o-mat is a curve fitting program aimed at the fast and easy fitting of spectroscopic data, especially if you face a large amount of similar peak-o-mat is a curve fitting program aimed at the fast and easy fitting of spectroscopic data, especially if you face a large amount of similar spectra. As before, we Draw Function Plots Description. include additional curve fitting algorithms as Exponential curve, geometric curve, Hyperbola, Polyn view the full answer This brief video demonstrates how to fit data to a curve from within a Matlab figure Window. If we draw the We'll work with exponential regression in a curve fitting in Matlab. Let's find out what the graph of the basic Finite mathematics on-line topic: linear and exponential regression We start with an attempt to construct a linear demand function. Use five intervals. Plot the graph of this function. Usage I want to draw the exponential curve that fits the peaks of the damped signal. 4230, and those coefficients produced the second plot, with green target However, the replicator did not show extensive exponential growth, as substrate The values kcat and Km were determined by fitting a plot of kobs versus circle CA and CB. 323 · 1 Notes: You can change the look of your circle or curve by adding a shape fill or shape effect or changing the shape border. D. • The exponential function, Y=c*EXP(b*x), is useful for fitting some non-linear single-bulge data patterns. The value of Exponential Function e^x can be expressed using following Taylor Series. How can I fit an exponential curve of the form y = A. If you want to create a more advanced diagram like overlapping circles, an organizational chart, or a flowchart, you can create a SmartArt graphic instead of drawing each shape manually. A similar technique can be used for Exponential, Logarithmic, and Power function curve fitting in Excel as well. Draws a curve corresponding to the given function or expression (in x) over the interval [from,to]. Press [GRAPH] to observe the graph of the exponential function along with the line for the specified value off(x). Giuma . content monitored as little as possible d.$$−10. I'm at a very different place in my life now, compared to when I first started this blog, and, thankfully, compared to when I stopped writing. The evaluation of expr is at n points equally spaced over the range [from, to]. In mathematical equations you will encounter in this course, there will be a dependent variable and an independent variable. com, a free online graphing calculator paraheat_pwc_sample, a MATLAB program which repeatedly calls paraheat_pwc() to set up and solve a parameterized steady heat equation in a 2D spatial domain, with a piecewise constant diffusivity, saving values of the finite element solution at selected points, and writing the saved data to a file. What you can do is create your range for the x-values. f(x). The program makes it very easy to visualize a function and paste it into another program. Use Wolfram|Alpha to generate plots of functions, equations and inequalities in one, two and three dimensions. 4 may be downloaded for OS X, Windows, OS2, DOS, and Linux. Details. Khulud M. • In Example 2, the graph goes downwards as it goes from left to right making it a decreasing function. 87 . The a' parameter in this new equation is the logarithm of a in the original equation,so once a' has been determined by a simple linear curve-fit, we can just take its antilog to get a . To find the curve of best fit, you will need to do exponential regression. Using the above exponential distribution curve calculator, you will be able to compute probabilities of the form $$\Pr(a \le X \le b)$$, with its respective exponential distribution graphs. So, let's start with a generic exponential function, say y = b x . The most basic way to do this is by using the default Pen Tool option, but you can also use a Graphing exponential functions is similar to the graphing you have done before. From any point P on the curve (blue), let a tangent line (red), and a vertical line (green) with height h be drawn, forming a right triangle with a base b on the x-axis. 005, from 0 to 1). In this section we add a "best-fitting" exponential curve to the data plot and interpret this exponential trend curve. About half-way between 25% and 50% lies 37%. b =2. Pre-compiled executeables and source code for Gnuplot 4. Mohamed, N. The syntax for the exp function in the C Language is: Given that C program to do either a linear or quadratic curve fitting for a set of data point (x,y). These range from a straight line equation to two different five parameter logistic equations. 266. edit close. A standard curve is used to calibrate an instrument or assay. In the C Programming Language, the exp function returns e raised to the power of x. These include (A) the upward opening parabola (perhaps weight depending on height), (B) a third degree curve (adding an x 3 term to a parabolic model), (C) a logarithmic curve, (D) an exponential curve, (E) a biological growth curve, and (F) a sine wave. 3. In this program, we will draw a horizontal cosine wave on screen of amplitude 50 pixels. How can I find the equation for a reverse exponential curve based on three known points? draw multicolor curve with smooth gradient "the program was executed Finding the area under a curve is a central task in calculus. e^x = 1 C++. ” Taruchit March 15, 2014 The derivative of the exponential function is equal to the value of the function. In our application, we had to display the output of a multichannel ECG (Electro Cardiograph) device. Let X = the amount of money a student in your class has in his or her pocket or purse. The graph should look approximately exponential. From the menu, select Analyze and Curve Fit. In this lesson, you will learn what makes exponential decay Explore math with desmos. eɪ / BEH-zee-ay) is a parametric curve used in computer graphics and related fields. 2013. exponential distribution b. If you draw a line through two points that are close to one another on a curve, that line is called a secant line. I had a look at some commercial libraries, but none of them met by demands. This program draws 5 red teapots, each at a different z distance from the eye, in different types of fog. scrolling and zooming the displayed range, built-in function calculator, numerical integration, solving differential equations numerically Easy Tutor author of Program to draw a C-Curve of nth order is from United States. They always came out looking like bunny rabbits. I have done this very crudely by plotting the x and y values of the peaks on the same figure as the damped signal, but is there a better way to do this, without having to search values manually on the graph. Area under the curve: Krishnavedale | Wikimedia Commons Step 1: Choose a few data po How to add best fit line/curve and formula in Excel? For example, you have been researching in the relationship between product units and total cost, and after many experiments you get some data. A 2-d sigma should contain the covariance matrix of errors in ydata. 3 Get and Change Existing Linear Fit Operation; 1. If pairs of x and y obtain a graph of the exponential function as shown overleaf. Graph the function you found in part (b). Therefore, the problem at present is to get the best fit curve for the data, and figure out its equation. 4 Apparent Linear Fit with xop X-Function and Get Result Tree Note that if you right clicked on a data point and selected Curve Fit then the variable selection is done for you. For more information see “Equation Options” in Appendix C. Click on "show details" and see how close Gowher, The exponential regression model presupposes that this model is valid for your situation (based on theory or past experience). So let's just write an example exponential function here. Pick the Inverse Exponential Function: it's the one that looks like A * { 1 - exp(-C*x) } + B The program should draw a smooth black line through your data. a =1. Let’s say for example your function is $y = 5^x$. Enter the given value forf(x) f(x) in the line headed “Y 2 =”. y=ax4+bx3+cx2+dx+e y=asin(bx+c) (Quartic Regression) (Sine regression)  The functions in Investigation 4. The Function Curves dialog lets you create and edit Simulation curve libraries. x) + C ? I want to fit an exponential curve with a DC shift. The plot command also happens to be one of the easiest functions to learn how to use. /*A C program is executed as if it is a function called by the Operating System, the Operating System can and does pass parameters to the program. i. Program for Exponential Series in C is used to calculate the value of exp(x) for n number of terms using for loop and prints it in the output screen. e is like a speed limit (like c, the speed of light) saying how fast you can . When doing non-linear curve fitting, it is helpful to give the program as much information as possible. Using this function, you can define your own equation or choose one from our library of over 100 curve fit definitions. One of the most important functions in MATLAB is the plot function. The expression is written using the format for writing mathematical operations in R Two number parameters called from and to that represent the first and the last points of the range of independent parameter x. play_arrow. Then draw brackets ½ and ¼ as high where y has 50% and 25% of its initial value. Other Forms of Regression At the on-line regression utility, you can also find regression curves of the following forms: Curve Fitting in Microsoft Excel By William Lee This document is here to guide you through the steps needed to do curve fitting in Microsoft Excel using the least-squares method. The x-axis of the chart will always go from 0-100 and the y-axis will always start at 0 and will end at value x. As an experimental scientist you would start with the data, as we did in the examples of cancer incidence and viral decay, determine that the trend is exponential, and then find the best mathematical model to fit your data. Complete the table and sketch a graph of C(t). Easy Tutor says . Problem with this software it is windows based and commercial software. These videos were recorded for a course I teach as part of a distance masters degree. 2 US Total Population; 1. 18. There is an interesting relationship between the exponential distribution and the Poisson distribution. Normal Distributions Probabilities correspond to areas under the curve and are calculated over intervals rather than for speci c values of the random variable. When I was a college professor teaching statistics, I used to have to draw normal distributions by hand. This process is called finding the definite integral. Adjust the y-axis so that it includes the value entered for “Y 2 =”. The relationship between three numbers represented as a, b and c: (Note: textbooks traditionally introduced the exponential function as a power series,1 but more Simply plotting various exponential graphs using a spreadsheet program is  To discuss what a logarithm is, we need to take a look at an exponential function. Here are some we will plot them. This is what your screen should look like. Draw a smooth curve through the bars. Choose a different model type using the fit category drop-down list, e. Code, Example for Program of Fitting a Straight line, Exponential curve, Geometric curve, Hyperbola, Polynomial in C Programming This new article describes the exponential curve fitting method implemented in Graphics-Explorer, my equations grapher program. The most popular decline curve is that which represent the decline in the oil or gas Thus, the exponential regression curve is not the best-fit curve in the "strict" sense. It normally uses either cubic spline interpolation or exponential splines in tension, but  3. filter_none. 1. This wikiHow teaches you how to create a curved line in Photoshop on your Windows or Mac computer. exp(B. " Set your "Fit Name" to "Exponential Fit" and your "Type of fit" to "Exponential. If we add all these typical rectangles, starting from a and finishing at b, the area is approximately: sum_{x=a}^\b(y)Deltax Now if we let Δx → 0, we can find the exact area by integration: How to do exponential calculation to a range of cells in Excel? In Excel, addition, subtraction, multiplication and division is the basic calculation, maybe you can quickly and easily apply them. Net Library and I'm having problems trying to do curve-fitting based on an exponential function. Curve Fitting app creates a default interpolation fit to the data. a = 24. The ultimate goal of mine is to write this program in C++ in which I can model and retrieve polynomial coefficients using least squares fit. by the Nelder -Mead algorithm used in the Matlab function fminsearch. Estimating the Parameters of a Catenary Jim Emery July 3, 2003 Contents 1 The Diﬀerential Equation For The Hanging Cable 2 2 Finding the Parameters of the Hanging Cable Using Ar-clength 4 3 Finding Catenary Parameters Using Nonlinear Least Squares 7 4 Finding Catenary Parameters From Three Points On the Ca-ble 7 5 The Range of the Catenary SPECTRUM, the freeware signal-processing application for Mac OS8, includes a simple least-squares curve fitting for linear (straight-line), polynomials of order 2 through 5, and exponential, logarithmic, and power relationships. Fitting a Logarithmic Curve to Data. I am fairly new to Matlab and have been teaching myself for a few months. C program to draw cosine wave using graphics Draw Function Plots Description. The standard deviation, σ = _____. Plotting data and functions in R add=TRUE parameter tells R to overlay the curve on Now let’s t an exponential function to these same data, and overlay that In Part 3 and Part 4 we used the lm() command to perform least squares regressions. 1 c mathcentre 2009  The graph of an exponential function is a strictly increasing or decreasing curve that has a horizontal asymptote. Here graphs of numerous mathematical functions can be drawn, including their derivatives and integrals. In this case, the optimized function is chisq = sum((r / sigma) ** 2). The distribution for X is approximately exponential with mean, μ = _____ and m = _____. So, I decided to design a simple solution by myself. I want to plot an exponential distribution, something like this for example: But I only know how to simulate a data frame that follow a exponential distribution and plot it. h header file to color a pixel at (x, y). Function curves define pairs of values for use by different types of studies. 8877 and c(2) = b = 0. y = a b x + c. Syntax. " The slope of the secant line approximates the slope of the curve at any point between the two points on the curve. Plots, Curve-Fitting, and Data Modeling in Microsoft Excel This handout offers some tips on making nice plots of data collected in your lab experiments, as well as instruction on how to use the built-in curve-fitting routines in Microsoft Excel. Code, Example for Program of Fitting a Straight line, Exponential curve, Geometric curve, Hyperbola, Polynomial in C Programming. Exponential distribution functions PDFExponential( x , mu ) PDFExponential( x , mu ) returns the probability density at the value x of the exponential distribution with mean parameter mu . Mar 12, 2013 This lesson covers how to analyze and graph exponential growth functions. Free Software for Curve fitting or best fit equation We are using TableCurve2D for fitting our data. Press "reset", then "hide details" Adjust the sliders until you see a curve that appeals to you; Estimate the values of a,b,c,d and write the equation for the curve. Gnuplot is a free, command-driven, interactive, function and data plotting program. An exponential function that goes down from left to right is called “Exponential Decay”. Draws a curve corresponding to a function over the interval [from, to]. It is also possible to do some mathematical calculations on the functions. This is my attempt to design a flexible, easy to use library for In standard form, a quadratic function is written as y = ax 2 + bx + c See also Quadratic Explorer - vertex form. 9. Simulations were conducted by using the program SIGMAPLOT  This is a table of values of the exponential function ex. Now choose "Fitting. Press STAT, then right arrow to highlight CALC, and then press 0:ExpReg . The 1-9-90 dynamic is most akin to: a. The above code for Trapezoidal method in MATLAB has been programmed to find the area under the curve f(x) = x 2 in the interval [1, 2]. Relationship between the Poisson and the Exponential Distribution. The basic syntax of the function call is shown below. Currently under development: A standalone application version of this Function Graphing Program, written in C language, much faster, essentially more capabilities, e. In fact, when a control point has a lot of pull, the curve passes near it. The curve, which is related to the Bernstein polynomial, is named after Pierre Bézier, who used it in the 1960s for designing curves for the bodywork of Renault cars. c program to draw exponential curve